This program aims to elucidate molecular events in early amphibian embryogenesis; a family of genes encoding embryo and larval specific keratins have been the primary focus of recent attention. Analysis of these genes has revealed the presence of three subfamilies, named XK70, XK81 (both acidic, type I keratins), and XK76 (a more basic, type II keratin). Genomic and/or cDNA clones have isolated for 4 members of the XK81 subfamily and 2 members of the XK70 subfamily. Genomic suquences obtained for 3 XK81 genes reveal conserved 5' flanking regions that could have regulatory functions. Genomic clones corresponding to XK70 have also been isolated and sequenced. Constructs containing the 5' flanking region from the XK81A1 gene attached to the CAT marker gene have been injected into frog embryos, resulting in expression during embryogenesis of CAT enzyme activity. The regions of accumulation of keratins and keratin mRNAs in the frog embryo have been studied by in situ hybridization and immunofluorescence. Keratin mRNA and keratins accumulate primarily in the outer layer of the ectoderm at early gastrula and the epidermis during subsequent differentiation. During gastrulation, neural induction of an ectodermal region by chrodamesoderm leads to formation of the central nervous system; this inductive event is accompanied by immediate cessation of keratin mRNA accumulation in this region. Regulation of keratin synthesis is the earliest available molecular marker for neural induction and provides an approach to the study of neurogenesis.